SONOMA, Calif.--In the race to build a new generation of energy-efficient cars, the spark plug may become one of the first casualties.

Toyota, General Motors and virtually every other major automobile manufacturer are tinkering with a technology called Homogeneous Charge Compression Ignition (HCCI), which could boost fuel economy in cars by about 20 percent and generate fewer polluting hydrocarbons. Research projects are also under way at national labs and universities.

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Automobile industry researchers and observers gathered recently to discuss fuel efficiency and alternatives to the internal combustion gasoline engine. They didn't always agree on what the best alternatives might be, but all acknowledged that current gas prices are adding urgency to the debate.

Bottom line:Diesel-powered cars and cars with gas-electric hybrid engines are likely to become much more common. Researchers also are exploring an internal combustion technology called Homogeneous Charge Compression Ignition, or HCCI, which could increase fuel efficiency by 20 percent and produce less pollution.

In HCCI, the combustion process occurs by moderating the pressure and temperature inside the cylinder. Igniting the fuel with a spark is not required, said John Pinson, group manager of diesel engine research at the General Motors Research and Development Center, said during a one-day symposium sponsored by Infineon Technologies. A similar, but slightly different and slightly less effective, combustion process takes place in diesel engines.

"It is more efficient and less far-fetched than it sounds," Pinson said of HCCI. "In this decade you are going to see incremental introduction of it."

Other near-term ideas include use of gasoline-electric hybrid engines and engines fueled by hydrogen, diesel and/or ethanol. All these options have their critics.

On one end of the spectrum, Karina Morley, director of powertrain control electronics at automotive-systems supplier Visteon, says that the gas burning engine's days are numbered.

"Within 10 years, you are going to see the transition to alternative fuel sources," she said. "Eventually internal combustion engines will die off, but it'll take 20 to 30 years."

Dave Hermance, executive engineer for advanced technology vehicles at Toyota USA, disagrees with that assessment. Internal combustion engines will probably still be going quite strong for 20 years, he said, and oil companies will still be producing petroleum products. Nonetheless, the rising cost of these products is going to make the alternatives attractive.

"The break-even point used to be $30 a barrel for alternative fuels. We're way past that," he said.

Diesel's advocates
For its part, GM is one of the primary backers of diesel fuel. Diesel provides about 12 percent more energy than standard gasoline, said Pinson. Improved engines will also likely make it possible for diesel cars to meet emission standards already laid out by the federal government in a cost-efficient way, he said.

Another advantage of diesel is that one of the basic elements of the fuel-supply infrastructure--gas stations--already exists. Diesel is already popular in Europe. While it's tougher to find diesel in the U.S., its popularity could grow. DaimlerChrysler's Mercedes has had excellent sales of its diesel cars, which it reintroduced to the U.S. market in 2004, said John McElroy, an automotive journalist who hosts the TV show American Driver. Audi also has committed to bringing diesel vehicles to the U.S.

Ultimately, GM would like to marry full-fledged HCCI to diesel for a higher level of fuel efficiency, according to Pinson. Some aspects of HCCI will come to cars sold in Europe in 2007, he said.

HCCI, with regular gas or diesel, will take quite a bit of work, Pinson acknowledged. The pressure and temperature inside the cylinder need to be minutely calibrated. Gas from different stations may differ slightly in composition and performance, and could turn a smooth-running HCCI engine into a pinging, coughing machine.

Since the quality of gas and other environmental factors can't be controlled, the solution is to control the pressure/temperature inside the cylinders with sensors that can send data to a microprocessor controlling the engine. To raise the temperature, for instance, the microprocessor can send signals to the engine that will cause it to retain some of the hot gases from previous combustions in the cylinder.